1. Field
The technical field relates to a thermoelectric module and a method for fabricating the same, and in particular to a thermoelectric module having segmented thermoelectric elements and a method for fabricating the same.
2. Description
Many homogeneous thermoelectric compounds suitable for different temperature ranges have been studied over decades, but no single homogeneous thermoelectric compound exhibits an uniform high figure-of-merit over a wide temperature range, e.g. such as between 80° C. and 600° C. This common shortcoming of such homogeneous thermoelectric materials limits the generation efficiency of prior art thermoelectric modules because of the low mean figure-of-merit.
In order to enhance the generation efficiency of the thermoelectric module, forming the segmented thermoelectric elements by bonding the appropriate homogeneous thermoelectric materials from suitable low-temperature to high-temperature range is a reasonable option. Processes of welding stacked heterogeneous bulk materials, hot-pressed bonding stacked heterogeneous bulk materials with fusion metallic filler, and hot-compression sintering stacked heterogeneous powder materials, can be used to fabricate the segmented thermoelectric elements/materials with higher thermal to electricity conversion efficiency.
However, the above-mentioned thermoelectric module will generate a high twist thermal stress/strain during a wide temperature gradient operation, resulting in the possibility of a peel-off between those segmented thermoelectric elements and corresponding electrodes and/or failure of segmented thermoelectric elements. Therefore, a segmented thermoelectric element with appropriate cushioned structure helps to accommodate the thermal stress. Among the feasible processes of segmented thermoelectric elements/materials, the fusion-bonding process is an option to meet the requirement, but several prerequisites can be reached.
The fusion process temperature can be as low as possible, in order to avoid the deterioration of figure-of-merit of the thermoelectric materials (for example, comprising highly volatile tellurium, and in order to avoid the phase transformation of the thermoelectric materials). The fusion-bonding layer formed at low process temperature maintains its thickness even in semi-solid state in order to withstand a higher service temperature, which is higher than the fusion process temperature. And, relationship related accommodating the thermal stress and fusion-bonding layer function as a cushion, the thicker the fusion-bonding layer is, and the lower Young's modulus of the fusion-bonding layer is, the more easily the fusion-bonding layer accommodates the thermal stress.
Accordingly, it is a trend to develop a thermoelectric module with novel segmented thermoelectric elements therein which are jointed by fusion-bonding process to withstand high service temperature.